According to the Centers for Disease Control and Prevention study, 13% of adults aged 18 to 64 save money by skipping doses, taking lower doses than prescribed or foregoing treatment altogether. Only 5.8% of patients 65 and older–in other words, Medicare beneficiaries–don't take their drugs as directed.

Obviously, anytime a patient chooses not to take drugs as prescribed, pharma loses sales, and there's the potential for costly care down the road, particularly with chronic illnesses like diabetes. One study estimated that pharma loses $ 564 billion globally to lax pill-taking. So, the industry is experimenting with reminders, technological and otherwise, to increase adherence. But a nudge from a text or a talking pill bottle might not inspire patients who are pinching pennies.

Some of that difference in pill-taking habits lies on the younger end of the spectrum, said Steve Morgan, an associate professor at the University of British Columbia. "Even among insured populations, there is this invincibility mindset among the very young," Morgan told Bloomberg.

But predictably, health coverage–or lack of it–played a big role. Uninsured adults were more likely to stretch their supplies of prescription drugs than patients covered by Medicaid or private insurance.